Furfural refining unit control system

ABSTRACT

A system controls a furfural refining unit in which the furfural refining unit includes an extractor receiving furfural and charge oil, one of which is at a predetermined flow rate while the other flow rate is to be controlled and providing raffinate and extract mix. The control system includes sensors sensing the flow rate, the gravity, the viscosity, the flash point temperature, the refractive index and the sulfur content of the charge oil. Other sensors sense the flow rate of the furfural and the temperature of the extract mix. The signals from the sensors are provided to control apparatus which controls the other flow rate of the charge oil and the furfural flow rates in accordance with the signals from the sensors.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation as to all subject matter common toU.S. application Ser. No. 851,999 filed Nov. 16, 1977, now abandoned, byAvilino Sequeira, Jr., John D. Begnaud and Frank L. Barger, and assignedto Texaco Inc., assignee of the present invention, and acontinuation-in-part for additional subject matter.

BACKGROUND OF THE INVENTION

The present invention relates to control systems in general and, moreparticularly, to control systems for oil refining units.

SUMMARY OF THE INVENTION

A furfural refining unit treats charge oil with a furfural in anextractor which provides raffinate and extract mix. The furfural isrecovered from the raffinate and from the extract mix and returned tothe extractor. A system controlling the refining unit includes a gravityanalyzer, a flash point temperature analyzer, viscosity analyzers, arefractive index analyzer and a sulfur content analyzer. The analyzersanalyze the charge oil and provide corresponding signals. Flow ratesensors sense the flow rates of the charge oil and the furfural enteringthe extractor and provide flow rate signals. One of the flow rates ofthe charge oil and the furfural flow rate is a constant flow rate whilethe other flow rate is controllable. The controllable flow rate iscontrolled in accordance with the signals provided by all the sensorsand the analyzers.

The objects and advantages of the invention will appear more fullyhereinafter from a consideration of the detailed description whichfollows, taken together with the accompanying drawings wherein oneembodiment of the invention is illustrated by way of example. It is tobe expressly understood, however, that the drawings are for illustrativepurposes only and are not to be construed as defining the limits of theinvention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a control system, constructed inaccordance with the present invention, for controlling an oil refiningunit shown in partial schematic form.

FIG. 2 is a simplified block diagram of the control means shown in FIG.1.

FIGS. 3 through 24 are simplified block diagrams of the H computer, theK signal means, the H signal means, the KV computer, the VI signalmeans, the SUS computer, the SUS₂₁₀ computer, the VI_(DWC).sbsb.Ocomputer, the J computer, the VI_(DWC).sbsb.P computer, the A computer,the J computer, the W computer, the VI_(DWC).sbsb.O computer, the Acomputer, the J computer, the J computer and the selection means,respectively, shown in FIG. 2.

DESCRIPTION OF THE INVENTION

An extractor 1 in a furfural refining unit receiving charge oil by wayof a line 4 and furfural solvent by way of a line 7 and providingraffinate to recovery by way of a line 10, and an extract mix torecovery by way of a line 14. The temperature in extractor 1 iscontrolled by cooling water passing through a line 16. A gravityanalyzer 29, flash point analyzer 22, viscosity analyzers 23 and 24, arefractometer 26 and a sulfur analyzer 28, sample the charge oil in line4 and provide signals API, FL, KV₂₁₀, KV₁₅₀, RI and S, respectively,corresponding to the API gravity, the flash point, the kinematicviscosity at 210° F., and the kinematic viscosity at 150° F., therefractive index and the sulfur content, respectively.

A flow transmitter 30 in line 4 provides a signal CHG corresponding tothe flow rate of the charge oil in line 4. Another flow transmitter 33in line 7 provides a signal SOLV corresponding to the furfural flowrate. A temperature sensor 38, sensing the temperature of the extractmix leaving extractor 1, provides a signal T corresponding to the sensedtemperature. All signals hereinbefore mentioned are provided to controlmeans 40.

Control means 40 provides signal C to a flow recorder controller 43.Recorder controller 43 receives signals CHG and C and provides a signalto a valve 48 to control the flow rate of the charge oil in line 4 inaccordance with signals CHG and C so that the charge oil assumes adesired flow rate. Signal T is also provided to temperature controller50. Temperature controller 50 provides a signal to a valve 51 to controlthe amount of cooling water entering extractor 1 and hence thetemperature of the extract-mix in accordance with its set point positionand signal T.

The following equations are used in practicing the present invention forlight sweet charge oil, that is a charge oil having a sulfur contentequal to or less than a predetermined sulfur content and having akinetic viscosity, corrected to a predetermined temperature, equal to orless than a first predetermined kinetic viscosity:

    1. H.sub.210 =1n1n(KV.sub.210 +C.sub.1)

where H₂₁₀ is a viscosity H value for 210° F., KV₂₁₀ is the kinematicviscosity of the charge oil at 210° F. and C₁ is a constant having apreferred value of 0.6.

    2. H.sub.150 =1n1n(KV.sub.150 +C.sub.1)

where H₁₅₀ is a viscosity H value for 150° F., and KV₁₅₀ is the kineticviscosity of the charge oil at 150° F.

    3. k.sub.150 =[c.sub.2 -1n(T.sub.150 +C.sub.3)]/C.sub.4

where K₁₅₀ is a constant needed for estimation of the kinematicviscosity at 100° F., T₁₅₀ is 150, and C₂ through C₄ are constantshaving preferred values of 6.5073, 460 and 0.17937, respectively.

    4. H.sub.100 =H.sub.210 +(H.sub.150 -H.sub.210)/K.sub.150

where H₁₀₀ is a viscosity H value for 100° F.

    5. kv.sub.100 =exp[exp(H.sub.100)]--C.sub.1

where KV₁₀₀ is the kinematic viscosity of the charge oil at 100° F.

    6. sus=c.sub.5 (kv.sub.210)+[c.sub.6 +c.sub.7 (kv.sub.210)]/[c.sub.8 +c.sub.9 (kv.sub.210)+c.sub.10 (kv.sub.210).sup.2 +c.sub.11 (kv.sub.210).sup.3 ](c.sub.12)

where SUS is a factor needed in equation 7 and C₅ through C₁₂ areconstants having preferred values of 4.6324, 1.0, 0.03264, 3930.2,262.7, 23.97, 1.646 and 10⁻⁵, respectively.

    7. SUS.sub.210 =[C.sub.13 +C.sub.14 (C.sub.15 -C.sub.16)]SUS

where SUS₂₁₀ is the viscosity in Saybolt Universal Seconds at 210° F.and C₁₃ through C₁₆ are constants having preferred values of 1.0,0.000061, 210 and 100, respectively.

    8. VI.sub.DWC.sbsb.O =C.sub.17 -C.sub.18 (FL)+C.sub.19 (VI)+C.sub.20 (KV.sub.210)(API)

where VI_(DWC).sbsb.O, FL, VI, and API are the viscosity index of thedewaxed product at zero pour point, the flash point temperature of thecharge oil, the viscosity index of the charge oil and the API gravity ofthe charge oil, respectively, and C₁₂ through C₂₀ are constants havingpreferred values of 27.35, 0.1159, 0.69819 and 0.21112, respectively.

    9. VI.sub.DWC.sbsb.P =VI.sub.DWC.sbsb.O +(Pour)[C.sub.21 -C.sub.22 lnSUS.sub.210 +C.sub.23 (1nSUS.sub.210).sup.2 ]

where VI_(DWC).sbsb.P and Pour are the viscosity index of the dewaxedproduct at a predetermined temperature and the Pour Point of the dewaxedproduct, respectively, and C₂₁ through C₂₃ are constants havingpreferred values of 2.856, 1.18 and 0.126, respectively.

    10. ΔVI=VI.sub.RO -VI.sub.DWC.sbsb.O =VI.sub.RP -VI.sub.DWC.sbsb.P

where VI_(RO) and VI_(RP) are the VI of the refined oil at 0° F., and atthe predetermined temperature, respectively.

    11. A=C.sub.24 -C.sub.25 (S)-C.sub.26 (S).sup.2 +C.sub.27 (KV.sub.210)(API)-C.sub.28 (KV.sub.210)(VI)-C.sub.29 (FL)(API)+C.sub.30 (FL)(S)+C.sub.31 (FL)(VI)

where S is the percent sulfur in the charge oil, and C₂₄ through C₃₁ areconstants having preferred values of 434.074, 88.98932, 22.6125,3.17397, 1.3905, 0.05033, 0.51586 and 0.01388.

    12. J={{C.sub.32 -C.sub.33 A+{[C.sub.33 A-C.sub.32 ].sup.2 -4[C.sub.34 -C.sub.35 A][-C.sub.36 +C.sub.37 √T-C.sub.38 (A)(√T)-ΔVI]}.sup.1/2 }/2[C.sub.34 -C.sub.35 (A)]}.sup.2

where J is the furfural dosage and C₃₂ through C₃₉ are constants havingpreferred values of 15.762, 0.075007, 0.25747, 0.0012087, 5.2479, 14.096and 0.056338.

    13. C=(SOLV)(100)/J

for light sour charge oil, that is a charge oil having a sulfur controlgreater than the predetermined sulfur contant and having temperaturecorrected kinematic viscosity equal to or less than the firstpredetermined kinematic viscosity, equations 1 through 10 and 13 areused. However, equation 12 is replaced by the following equation 14.

    14. J={{-C.sub.39 +{(C.sub.39).sup.2 -4(C.sub.40)(T)[-C.sub.41 +C.sub.42 √T-ΔVI]}.sup.1/2 }/2[C.sub.40 T]}.sup.2

where C₃₉ through C₄₂ are constants having preferred values of 3.0093,0.00023815, 54.88 and 5.3621, respectively.

For medium sweet charge oil, that is a charge oil having a sulfurcontent equal to or less than the predetermined sulfur content andhaving a temperature corrected kinematic viscosity greater than thefirst predetermined kinematic viscosity but equal to or less than asecond predetermined kinematic viscosity, equations 1 through 7, 9, 10and 13 are used, along with the following four equations:

    15. W=C.sub.43 -C.sub.44 API+C.sub.45 /KV.sub.210 -C.sub.46 S+C.sub.47 (API).sup.2 -C.sub.48 API/KV.sub.210 +C.sub.49 (S) (API)

where W is the percent wax in the charge oil, and C₄₃ through C₄₉ areconstants having preferred values of 51.17 4.3135, 182.83, 5.2388,0.101, 6.6106 and 0.19609, respectively.

    16. VI.sub.DWC.sbsb.O =C.sub.50 -C.sub.51 RI+C.sub.52 (RI)(VI)+C.sub.53 (FL)(API)-C.sub.54 (W)(VI)

where C₅₀ through C₅₄ are constants having preferred values of 2306.54,1601.786, 1.33706, 0.00945 and 0.20915, respectively.

    17. A=C.sub.55 -C.sub.56 (API)+C.sub.57 (FL)(KV.sub.210)

where C₅₅ through C₅₇ are constants having preferred values of 860.683,28.9516 and 0.02389, respectively.

    18. J={{-C.sub.58 A+{(C.sub.58 A).sup.2 -4C.sub.59 A(C.sub.60 +C.sub.61 √T-ΔVI)}.sup.1/2 }/2C.sub.59 A}.sup.2

where C₅₈ through C₆₁ are constants having preferred values of 0.013795,-0.00025376, -18.233 and 1.1031, respectively.

Medium sour charge oil is a charge oil having a sulfur content greaterthan the predetermined sulfur content and having a temperature correctedkinematic viscosity greater than the first predetermined kinematicviscosity but equal to or less than the second predetermined kinematicviscosity.

For medium sour charge oil, equations 1 through 7, 9, 10, 13, 15, 16 and17 are used along with the following equation:

    19. J={{-C.sub.62 +{(C.sub.62).sup.2 -4(-C.sub.63)[C.sub.64 √T+C.sub.65 (√T)(A)-C.sub.66 -ΔVI]}.sup.1/2 }/2(-C.sub.63)

where C₆₂ through C₆₆ are constants having preferred values of 4.5606,0.085559, 1.8965, 0.0062567 and 55.744, respectively.

Heavy sweet charge oil is charge oil having a sulfur content equal to orless than the predetermined sulfur content and having a temperaturecorrected kinematic viscosity greater than the second predeterminedkinematic viscosity.

For heavy sweet charge oil, equations 1 through 7, 9, 10, 13 and 15 areused as well as the following equations:

    20. i VI.sub.DWC.sbsb.O =-C.sub.67 +C.sub.68 (KV.sub.210).sup.2 +C.sub.69 (VI)-C.sub.70 (API)(VI)+C.sub.71 (API).sup.2 +C.sub.72 (FL)(VI)-C.sub.73 (W)(KV.sub.210)

where C₆₇ through C₇₃ are constants having preferred values of 168.538,0.0468, 3.63863, 0.17523, 0.41542, 0.00106 and 0.21918, respectively.

    21. A=C.sub.74 -C.sub.75 (KV.sub.210).sup.2 +C.sub.76 (S)+C.sub.77 (FL).sup.2 -C.sub.78 (FL)(API)-C.sub.79 (KV.sub.210)(S)

where C₇₄ through C₇₉ are constants having preferred values of 503.518,0.04423, 54.58305, 0.00055, 0.03745 and 1.38869, respectively.

    22. J=(ΔVI-C.sub.80 -C.sub.81 √T)/[-C.sub.82 T+C.sub.83 (A)(T)]

where C₈₀ through C₈₃ have preferred values of 10.272, 1,0194,0.00067611 and 0.0000040229, respectively.

Heavy sour charge oil is a charge oil having a sulfur content greaterthan the predetermined sulfur content and having a temperature correctedkinematic viscosity greater than the second predetermined kinematicviscosity.

For heavy sour charge oil, equations 1 through 7, 9, 10, 13, 15, 20 and21 and the following equation 23.

    23. J={{-C.sub.84 (A)+{[C.sub.84 (A)].sup.2 -4[C.sub.85 (A)(T)][-C.sub.86 +C.sub.87 (A)(√T)-ΔVI]}.sup.1/2 }/2[C.sub.85 (A)(T)]}.sup.2

where C₈₄ through C₈₇ are constants 0.004074, 5.275×10⁻⁷ 13.199 and0.0059403, respectively.

Referring now to FIG. 2, signal KV₂₁₀ is provided to an H computer 50 incontrol means 40, while signal KV₁₅₀ is applied to an H computer 50A. Itshould be noted that elements having a number and a letter suffix aresimilar in construction and operation as to those elements having thesame numeric designation without a suffix. All elements in FIG. 2,except elements whose operation is obvious, will be disclosed in detailhereinafter. Computers 50 and 50A provide signals E₁ and E₂corresponding to H₂₁₀ and H₁₅₀, respectively, in equations 1 and 2,respectively, to H signal means 53. K signal means 55 provides a signalE₃ corresponding to the term K₁₅₀ in equation 3 to H signal means 53. Hsignal means 53 provides a signal E₄ corresponding to the term H₁₀₀ inequation 4 to a KV computer 60 which provides a signal E₅ correspondingto term KV₁₀₀ in accordance with signal E₄ and equation 5 as hereinafterexplained.

Signals E₅ and KV₂₁₀ are applied to VI signal means 63 which provides asignal E₆ corresponding to the viscosity index.

An SUS computer 65 receives signal KV₂₁₀ and provides a signal E₇corresponding to the term SUS in accordance with the received signalsand equation 6 as hereinafter explained.

An SUS 210 computer 68 receives signal E₇ and supplies signal E₈corresponding to the term SUS₂₁₀ in accordance with the received signaland equation 7 as hereinafter explained.

A VI_(DWC).sbsb.O computer 70 receives signal KV₂₁₀, API, FL and E₆ andprovides a signal E₉ corresponding to the term VI_(DWC).sbsb.O inaccordance with the received signals and equation 8 as hereinafterexplained.

A VI_(DWC).sbsb.P computer 72 receives signal E₈ and E₉ and provides asignal E₁₀ corresponding to the term VI_(DWC).sbsb.P in accordance withthe received signals and equation 9. Subtracting means 76 performs thefunction of equation 10 by subtracting signal E₁₀ from voltage V₉corresponding to the term VI_(RP), in equation 10, to provide a signalE₁₁ corresponding to the term ΔVI in equation 10.

An A computer 78 receives signals API, KV₂₁₀, S, FL and E₆ and provide asignal E₁₂ corresponding to a term A, in accordance with the receivedsignals and equation 11, as hereinafter explained.

A J computer 80 receives signals T, E₁₁ and E₁₂ and provides a signalE₁₃ corresponding to the term J in accordance with the received signalsand equation 12 as hereinafter explained.

It should be noted that the J factor just previously described, is forlight sweet charge oil. As the rest of the operation of control means 40continues to be described it will be noted that there will be a J factorsignal for each of the different types of charge oil, that is, lightsweet charge oil, light sour charge oil, medium sweet charge oil, mediumsour charge oil, heavy sweet charge oil and heavy sour charge oil. Itwill be appreciated that since there is no previous switching being donethat each J computer will provide a J factor signal, so that there willbe six J factor signals. However, only one of them is a correct andproper signal and that one signal being associated with the charge oilthat is in line 4. Therefore, the J signals such as signal E₁₃, areapplied to selection means 81, which will be described in greater detailhereinafter. Selection means 81 selects the proper J signal asdetermined in accordance with the signals KV₂₁₀ and S and provides theselected J signal to a divider 84. A multiplier 85 multiplies signalSOLV with a direct current voltage V₂ corresponding to a value of 100 toprovide a signal corresponding to the term (SOLV)(100) in equation 13.The signal from multiplier 85 is divided into the signal from selectionmeans 81 to provide signal C.

Another J computer 88 provides a signal E₁₅ corresponding to the Jfactor in equation 14 for light sour charge oil. J computer 88 receivessignals E₁₁ and T and provide signal E₁₅ in accordance with the receivedsignal and equation 14.

A W computer 90 receives signals KV₂₁₀, S and API and provides a signalE₁₆ corresponding to the term W in equation 15 in accordance with thereceived signals and equation 15 as hereinafter explained.

Another VI_(DW).sbsb.O computer 93 receives signals RI, FL, API, E₆ andE₁₆ and provides a signal E₁₇ corresponding to the term VI_(DWC).sbsb.Oin equation 16 in accordance with the received signals and equation 16as hereinafter explained. A VI_(DWC) _(P) computer 72A provides a signalE₁₈ corresponding to the term VI_(DWC) _(P) in equation 9, in accordancewith signals E₈ and E₁₇ and equation 9. Subtracting means 76A subtractssignal E₁₈ from voltage V₉ to provide a signal E₁₉ corresponding to theterm ΔVI in equation 10.

An A computer 95 receives signals KV₂₁₀, API and FL and provides asignal E₂₀ corresponding to the term A in equation 17, in accordancewith the received signals and equation 17 as hereinafter explained. A Jcomputer 97 receives signals T, E₁₉ and E₂₀ and provides a signal E₂₁corresponding to the J factor in equation 18 for medium sweet charge oilin accordance with the received signals and equation 18 as hereinafterexplained. Signal E₂₁ is applied to selection means 81.

Another J computer 98 receives signals T, E₂₀ and E₁₉ to provide asignal E₂₂ corresponding to the J factor in equation 19 for medium sourcharge oil in accordance with the received signals and equation 19 ashereinafter explained. Signal E₂₂ is supplied to selection means 81.

A VI_(DWC).sbsb.O computer 100 receives signals KV₂₁₀, API, FL, E₆ andE₁₆ and provides a signal E₂₃ corresponding to the term VI_(DWC).sbsb.Oin equation 20, in accordance with the received signals and equation 20as hereinafter explained.

A VI_(DWC).sbsb.P computer 72B provides a signal E₂₄ corresponding tothe term VI_(DWC).sbsb.P in equation 9 in accordance with the receivedsignal, signal E₈ and equation 9. Subtracting means 76B subtracts signalE₂₄ from voltage V₉ to provide a signal E₂₅ corresponding to the termΔVI in equation 10.

An A computer 104 receives signals KV₂₁₀, API, FL and S and provides asignal E₂₆ corresponding to the term A in equation 21 in accordance withthe received signals and equation 21.

A J computer 107 receives signals T, E₂₅ and E₂₆ to provide a signal E₂₇corresponding to the J term for heavy sweet charge oil in equation 22 inaccordance with the received signals and equation 22. Signal E₂₇ isapplied to selection means 81.

A J computer 110 receives signals T, E₂₅ and E₂₆ to provide a signal E₂₈corresponding to the J factor for heavy sour charge oil in accordancewith the received signal in equation 23, as hereinafter explained.Signal E₂₈ is provided to selection means 81.

Referring now to FIG. 3, H computer 50 includes summing means 112receiving signal KV₂₁₀ and summing it with a direct current voltage C₁to provide a signal corresponding to the term [KV₂₁₀ +C₁ ] shown inequation 1. The signal from summing means 112 is applied to a naturallogarithm function generator 113 which provides a signal correspondingto the natural log of the sum signal which is then applied to anothernatural log function generator 113A which in turn provides signal E₁.

Referring now to FIG. 4, K signal means 55 including summing means 114summing direct current voltages T₁₅₀ and C₃ to provide a signalcorresponding to the term [T₁₅₀ +C₃ ] which is provided to a natural logfunction generator 113B which in turn provides a signal corresponding tothe natural log of the sum signal from summing means 114. Subtractingmeans 115 subtracts the signal provided by function generator 113B froma direct current voltage C₂ to provide a signal corresponding to thenumerator of equation 3. A divider 116 divides the signal fromsubtracting means 115 with a direct current voltage C₄ to provide signalE₃.

Referring now to FIG. 5, H signal means 53 includes subtracting means117 which subtracts signal E₁ from signal E₂ to provide a signalcorresponding to the term H₁₅₀ -H₂₁₀, in equation 4, to a divider 118.Divider 118 divides the signal from subtracting means 117 by signal E₃.Divider 118 provides a signal which is summed with signal E₁ by summingmeans 119 to provide signal E₄ corresponding to H₁₀₀.

Referring now to FIG. 6, a direct current voltage V₃ is applied to alogarithmic amplifier 120 in KV computer 60. Direct current voltage V₃corresponds to the mathematical constant e. The output from amplifier120 is applied to a multiplier 122 where it is multiplied with signalE₄. The product signal from multiplier 122 is applied to an antilogcircuit 125 which provides a signal corresponding to the term exp [H₁₀₀] in equation 5. The signal from circuit 125 is multiplied with theoutput from logarithmic amplifier 120 by a multiplier 127 which providesa signal to antilog circuit 125A. Signal 125A is provided to subtractingmeans 128 which subtracts a direct current voltage C₁ from signal 125Ato provide signal E₅.

Referring now to FIG. 7, VI signal means 63 is essentially memory meanswhich is addressed by signals E₅, corresponding to KV₁₀₀, and signalKV₂₁₀. In this regard, a comparator 130 and comparator 130A represent aplurality of comparators which receive signal E₅ and compare signal E₅to reference voltages, represented by voltages R₁ and R₂, so as todecode signal E₅. Similarly, comparators 130B and 130C represent aplurality of comparators receiving signal KV₂₁₀ which compare signalKV₂₁₀ with reference voltages RA and RB so as to decode signal KV₂₁₀.The outputs from comparators 130 and 130B are applied to an AND gate 133whose output controls a switch 135. Thus, should comparators 130 and130B provide a high output, AND gate 133 is enabled and causes switch135 to be rendered conductive to pass a direct current voltage V_(A),corresponding to a predetermined value, as signal E₆ which correspondsto VI. Similarly, the outputs of comparators 130 and 130C control an ANDgate 133A which in turn controls a switch 135A to pass or to block adirect current voltage V_(B). Similarly, another AND gate 133B iscontrolled by the outputs from comparators 130A and 130B to control aswitch 135B so as to pass or block a direct current voltage V_(C).Again, an AND gate 133C is controlled by the outputs from comparators130A and 130C to control a switch 135C to pass or to block a directcurrent voltage V_(D). The outputs of switches 135 through 135C are tiedtogether so as to provide a common output.

Referring now to FIG. 8, the SUS computer 65 includes multipliers 136,137 and 138 multiplying signal KV₂₁₀ with direct current voltages C₉, C₇and C₅, respectively, to provide signals corresponding to the terms C₉(KV₂₁₀), C₇ (KV₂₁₀) and C₅ (KV₂₁₀), respectively in equation 6. Amultiplier 139 effectively squares signal KV₂₁₀ to provide a signal tomultipliers 140, 141. Multiplier 140 multiplies the signal frommultiplier 139 with a direct current voltage C₁₀ to provide a signalcorresponding to the term C₁₀ (KV₂₁₀)² in equation 6. Multiplier 141multiplies the signal from multiplier 139 with signal KV₂₁₀ to provide asignal corresponding to (KV₂₁₀)³. A multiplier 142 multiplies the signalfrom multiplier 141 with a direct current voltage C₁₁ to provide asignal corresponding to the term C₁₁ (KV₂₁₀)³ in equation 6. Summingmeans 143 sums the signals from multipliers 136, 140 and 142 with adirect current voltage C₈ to provide a signal to a multiplier 144 whereit is multiplied with a direct current voltage C₁₂. The signal frommultiplier 137 is summed with a direct current voltage C₆ by summingmeans 145 to provide a signal corresponding to the term [C₆ +C₇(KV₂₁₀)]. A divider 146 divides the signal provided by summing means 145with the signal provided by multiplier 144 to provide a signal which issummed with the signal from multiplier 138 by summing means 147 toprovide signal E₇.

Referring now to FIG. 9, SUS₂₁₀ computer 68 includes subtracting means148 which subtracts a direct current voltage C₁₆ from another directcurrent voltage C₁₅ to provide a signal corresponding to the term (C₁₅-C₁₆) in equation 7. The signal from subtracting means 148 is multipliedwith a direct current voltage C₁₄ by a multiplier 149 to provide aproduct signal which is summed with another direct current voltage C₁₃by summing means 150. Summing means 150 provides a signal correspondingto the term [C₁₃ +C₁₄ (C₁₅ -C₁₆ ] in equation 7. The signal from summingmeans 150 is multiplied with signal E₇ by a multiplier 152 to providesignal E₈.

Referring now to FIG. 10, there is shown VI_(DWC).sbsb.O computer 70having a multiplier 156 multiplying signals KV₂₁₀ and API to provide asignal corresponding to the term (KV₂₁₀) (API) in equation 8. Anothermultiplier 157 multiplies the signal from multiplier 156 with directcurrent voltage C₂₀ to provide a signal corresponding to the term C₂₀(KV₂₁) (API). A multiplier 160 multiplies signal E₆ with direct currentvoltage C₁₉ to provide a signal corresponding to the term C₁₉ (VI).Summing means 162 sums the signals from multiplies 157 and 160 with adirect current voltage C₁₇ to provide a sum signal. Multiplier 164multiplies signal FL with direct current voltage C₁₈ to provide a signalcorresponding to the term C₁₈ (FL) in equation 8. Subtracting means 165subtracts the signal provided by multiplier 164 from the signal providedby summing means 162 to provide signal E₉.

VI_(DWC).sbsb.P computer 72 shown in FIG. 11, includes a naturallogarithm function generator 168 receiving signal E₈ and providing asignal corresponding to the term lnSUS₂₁₀ to multipliers 170 and 171.Multiplier 170 multiplies the signal from function generator 168 with adirect current voltage C₂₂ to provide a signal corresponding to the termC₂₂ lnSUS₂₁₀ in equation 9. Multiplier 171 effectively squares thesignal from function generator 168 to provide a signal that ismultiplied with the direct current voltage C₂₃ by a multiplier 175.Multiplier 175 provides a signal corresponding to the term C₂₃(lnSUS₂₁₀)² in equation 9. Subtracting means 176 subtracts the signalsprovided by multiplier 170 from the signal provided by multiplier 175.Summing means 177 sums the signal from subtracting means 176 with adirect current voltage C₂₁. A multiplier 178 multiplies the sum signalsfrom summing means 177 with a direct current voltage POUR to provide asignal which is summed with signal E₉ by summing means 180 whichprovides signal E₁₀.

Referring now to FIG. 12, A computer 78 includes multipliers 182, 184multiplying signal S with a direct current voltage C₂₅ and signal FL,respectively, to provide signals corresponding to the term C₂₅ (S) and(FL) (S), respectively, in equation 11. The signal from multiplier 184is multiplied with a direct current voltage C₃₀ to provide a signalcorresponding to the term C₃₀ (FL) (S) by a multiplier 185. A multiplier186 effectively squares signal S and provides it to a multiplier 187where it is multiplied with a direct current voltage C₂₆ to provide asignal corresponding to the term C₂₆ (S)². Signal FL is also applied tomultipliers 190, 191 where it is multiplied with signals E₆ and API,respectively, to provide product signals to multipliers 194 and 195,respectively. Multipliers 194, 195 multiply the received signals withdirect current voltages C₃₁ and C₂₉, respectively, to provide signalscorresponding to the terms C₃₁ (FL) (VI) and C₂₉ (FL) (API) in equation11. Signal API is also multiplied with signal KV₂₁₀ by a multiplier 197and its product signal is provided to another multiplier 200 where it ismultiplied with a direct current voltage C₂₇. Multiplier 200 provides asignal corresponding to the term C₂₇ (K₂₁₀) (API). A multiplier 202multiplies signal E₆ with signal KV₂₁₀ to provide a signal to amultiplier 203 where it is multiplied with a direct current voltage C₂₈.Multiplier 203 multiplies a signal corresponding to the term C₂₈ (KV₂₁₀)(VI). Summing means 205 in summing the signals from multipliers 182,187, 195 and 203 in effect in summing all of the negative terms inequation 11 and provides them to subtracting means 206. Summing means207 is summing the outputs from multipliers 185, 194 and 200 with adirect current voltage C₂₄ in effect is summing all of the positiveterms in equation 11 to provide them to subtracting means 206 where thesignal from summing means 205 is subtracted from it to provide signalE₁₂.

In FIG. 13, J computer 80 includes multipliers 210, 211 multiplyingsignal E₁₂ with direct current voltages C₃₃ and C₃₅, respectively, toprovide signals corresponding to the terms C₃₃ A and C₃₅ A in equation12, respectively. The signal from multiplier 210 is subtracted from adirect current voltage C₃₂ by subtracting means 212, while subtractingmeans 214 subtracts voltage C₃₂ from the signal provides by multiplier210. Thus, subtracting means 212, 214 provide signals corresponding tothe terms C₃₃ A-C₃₂ and C₃₂ -C₃₃ A, respectively, in equation 12. Amultiplier 215 effectively squares the signal from subtracting means 214to provide a signal to subtracting means 218.

The signal provided by multiplier 211 is subtracted from a directcurrent voltage C₃₄ by subtracting means 220 to provide a signalcorresponding to the term [C₃₄ -C₃₅ (A)] in equation 12. Multipliers 222and 223 multiply the signal from subtracting means 220 with directcurrent voltages V₂₃ and V₄, corresponding to the values of 2 and 4, toprovide product signals. Signal T is applied to a conventional typesquare root circuit 225 which provides a signal to multipliers 226, 227where the signal is multiplied with signal E₁₂ and direct currentvoltage C₃₇, respectively. Multipliers 226 and 227 provide signalscorresponding to the term (A) (√T) and to C₃₇ √T, respectively, inequation 12. The signal from multiplier 226 is multiplied with a directcurrent voltage C₃₈ by a multiplier 230 which provides a signal tosumming means 233 where it is summed with another direct current voltageC₃₆ and a signal E₁₁ by summing means 233. Summing means 233 effectivelysums the negative terms which are shown as being -C₃₆, -C₃₈ (A) (√T) and-ΔVI.

Subtracting means 234 subtracts the signal provided by summing means 233from the signal provided by multiplier 227 to provide a differencesignal. A multiplier 236 multiplies the signal from multiplier 223 andsubtracting means 234 to provide a signal which is subtracted from thesignal provided by multiplier 215 by subtracting means 218. Subtractingmeans 218 provides a signal to a square root circuit 238 which providesa signal to summing means 240. Summing means 240 adds a signal providedby subtracting means 212 to the signal provided by square root circuit238. A divider 241 divides the signal from multiplier 222 into a signalprovided by summing. Dividing means 241 provides a signal that iseffectively squared by a multiplier 242 to provide signal E₁₃.

Referring now to FIG. 14, J computer 88 includes a square root circuit245 receiving signal T and providing a signal to a multiplier 246 whereit is multiplied with a direct current voltage C₄₂. Signal E₁₁ is summedwith a direct current voltage C₄₁ by summing means 250 to provide a sumsignal to subtracting means 251. Subtracting means 251 subtracts thesignal provided by summing means 250 from the signal provided bymultiplier 246. A multiplier 254 multiplies signal T with a directcurrent voltage C₄₀ to provide a signal to multipliers 256, 257 whichmultiplies the signal with direct current voltages V₄ and V₂₃,corresponding to values of 4 and 2, respectively. Multiplier 256provides a signal, corresponding to the term 4(C₄₀) (T) in equation 14,to a multiplier 258 where it is multiplied with the signal fromsubtracting means 251.

A multiplier 260 effectively squares a direct current voltage C₃₉ toprovide a signal corresponding to the term (C₃₉)² in equation 14.Subtracting means 262 subtracts the signal provided by multiplier 258from the signal provided by multiplier 260 to provide a signal to asquare root circuit 263. Subtracting means 265 subtracts voltage C₃₉from the signal provided by square root circuit 263 to provide a signalto a divider 266. Divider 266 divides the signal from subtracting means265 with the signal from multiplier 257 to provide a signal that iseffectively squared by a multiplier 267 to provide signal E₁₅.

Referring now to FIG. 15, there is shown W computer 90 havingmultipliers 270, 271 and 272 receiving signal API. Multiplier 270multiplies signal API with signal S to provide a product signal toanother multiplier 275 where it is multiplied with a direct currentvoltage C₄₉ to provide a signal corresponding to the term C₄₉ (S) (API)in equation 15. Multiplier 271 effectively squares signal API andprovides a signal to another multiplier 278 where it is multiplied witha direct current voltage C₄₇ to provide a signal corresponding to theterm C₄₇ (API)². Multiplier 272 multiplies signal API with a directcurrent voltage C₄₄ to provide a signal corresponding to the term C₄₄(API). A divider 280 divides signal API with signal KV₂₁₀ to provideanother signal to a multiplier 282 where it is multiplied with a directcurrent voltage C₄₈, which in turn provides a signal corresponding tothe term [C₄₈ (API)/(KV₂₁₀)] in equation 15. A divider 285 divides adirect current voltage C₄₅ with signal KV₂₁₀ to provide a signalcorresponding to the term C₄₅ /(KV₂₁₀). A multiplier 288 multipliessignal S with a direct current voltage C₄₆. Summing means 290 sums adirect current voltage C₄₃ with the signals provided by multipliers 275,278 and divider 285. Other summing means 291 sums the signals providedby multipliers 272, 282 and 288. Subtracting means 293 subtracts thesignal provided by summing means 291 from the signal provided by summingmeans 290 to provide signal E₁₆.

Referring now to FIG. 16, VI_(DWC).sbsb.O computer 93 includes amultiplier 300 receiving signals E₆, E₁₆ and providing a product signalto another multiplier 302 where it is multiplied with a direct currentvoltage C₅₄. Multiplier 302 provides a signal corresponding to the termC₅₄ (W) (VI) in equation 16. Another multiplier 305 multiplies signal RIwith a direct current voltage C₅₁ to provide a signal corresponding tothe term (C₅₁) (RI). Summing means 308 sums the signals from multipliers302, 305.

A multiplier 310 multiplies signals E₆ and RI to provide a productsignal to another multiplier 313 where it is multiplied with a directcurrent voltage C₅₂. Multiplier 313 provides a product signal to summingmeans 318. Another multiplier 320 multiplies signals FL and API toprovide a product signal to a multiplier 322 where it is multiplied witha direct current voltage C₅₃. Multiplier 322 provides a signalcorresponding to the term C₅₃ (FL) (API) in equation 16 to summing means318 where it is summed with the signal from multiplier 315 and a directcurrent voltage C₅₀ to provide a sum signal. Subtracting means 325subtracts the sum signal provided by summing means 308 from the signalprovided by summing means 318 to provide signal E₁₇.

Referring now to FIG. 17, A computer 95 includes a multiplier 330multiplying signal API with a direct current voltage C₅₆ to provide asignal corresponding to the term C₅₆ (API) in equation 17. Anothermultiplier 333 multiplies signals FL and KV₂₁₀ to provide a productsignal to a multiplier 335 where it is multiplied with a direct currentvoltage C₅₇. Multiplier 335 provides a product signal corresponding tothe term C₅₇ (FL) (KV₂₁₀) in equation 17 to summing means 338. Summingmeans 338 sums the signal provided by multiplier 335 with a directcurrent voltage C₅₅ to provide a sum signal. Subtracting means 340subtracts the signal provided by multiplier 330 from the sum signalprovided by summing means 338 to provide signal E₂₀.

Referring now to FIG. 18, J computer 97 includes multipliers 345 and 346multiplying signal E₂₀ with direct current voltages C₅₈ and C₅₉,respectively. Multiplier 348 effectively squares the signal provided bymultiplier 345 to provide a signal corresponding to the term (C₅₈ A)² tosubtracting means 354. Multiplier 350 multiplies the signal frommultiplier 346 with a direct current voltage V₄ corresponding to a valueof 4 to provide a product signal to another multiplier 356.

A square root circuit 360 receives signal T and provides a signalcorresponding to √T to a multiplier 233 where it is multiplied with adirect current voltage C₆₁. Multiplier 363 provides a product signal tosubtracting means 367 where signal E₁₉ corresponding to ΔVI issubtracted from it to provide a difference signal. Summing means 370sums the difference signal from subtracting means 367 with directcurrent voltage C₆₀ to provide a signal corresponding to the term [C₆₀+C₆₁ (T)^(1/2) -ΔVI] in equation 18 to multiplier 356. Multiplier 356multiplies the signal provided by multiplier 350 with the signalprovided by summing means 370 to provide a signal to subtracting means354 where it is subtracted from the signal provided by multiplier 348.Subtracting means 354 provides a difference signal to a square rootcircuit 376 which provides a signal to subtracting means 380.Subtracting means 380 subtracts the signal provided by multiplier 345from the signal provided by square root circuit 376 to provide a signalto a divider 383. A multiplier 385 multiplies a direct current voltageV.sub. 23, corresponding to a value of 2, with the signal provided bymultiplier 346 to provide a product signal to divider 383 where it isdivided into the signal provided by subtracting means 380. Divider 383provides signal E₂₁.

Referring now to FIG. 19, J computer 98 includes a square root circuit388 receiving signal T to provide a signal to multipliers 390 and 391.Multiplier 390 multiplies the signal from square root circuit 388 with adirect current voltage C₆₄ to provide a signal corresponding to the termC₆₄ T in equation 19. Multiplier 391 multiplies the signal from squareroot circuit 388 with signal E₂₀ to provide a signal to anothermultiplier 393 where it is multiplied with a direct current voltage C₆₅.Multiplier 393 provides a signal corresponding to the term C₆₅ (T)(A) inequation 19. Summing means 395 sums the signals from multipliers 390,393 to provide a sum signal to subtracting means 397. Summing means 400sums signal E₁₉ with a direct current voltage C₆₆ to provide a signalwhich is subtracted from the signal provided by summing means 395 bysubtracting means 397. A multiplier 402 multiplies direct currentvoltages C₆₃ and V₄ to provide a signal to another multiplier 403 whereit is multiplied with the signal provided by subtracting means 397. Amultiplier 405 effectively squares direct current voltage C₆₂ andprovides it to subtracting means 407. Subtracting means 407 subtractsthe signal from multiplier 403, from the signal from multiplier 405 andprovides a signal to a square root circuit 409. Subtracting means 410subtracts voltage C₆₂ from the signal provided by square root circuit409 to provide a signal to a divider 411. A multiplier 412 multipliesvoltages C₆₃ and V₂₃ to provide a signal to divider 411 which divides itinto the signal from subtracting means 410. The signal provided bydivider 411 is effectively squared by multiplier 414 to provide signalE₂₂.

Referring now to FIG. 20, a multiplier 418 effectively squares signalKV₂₁₀ and provides it to a multiplier 420 where it is multiplied withdirect current voltage C₆₈. Multiplier C₄₂₀ provides a signalcorresponding to the term C₆₈ (KV₂₁₀)² in equation 20. A multiplier 422multiplies signals KV₂₁₀, E₁₆ to provide a signal to another multiplier423 where it is multiplied with direct current voltage C₇₃. Multiplier423 provides a signal corresponding to the term C₇₃ (W) (KV₂₁₀) inequation 20. A multiplier 425 multiplies signal E₆ with a direct currentvoltage C₆₉ to provide a signal corresponding to the term C₆₉ (VI) inequation 20. Another multiplier 427 multiplies signals E₆, FL to providea signal to a multiplier 428 where it is multiplied with a directcurrent voltage C₇₂. Multiplier 428 provides a signal corresponding tothe term C₇₂ (FL) (VI) in equation 20. A multiplier 430 multipliessignals E₆ and API to provide a signal to another multiplier 431 whereit is multiplied with direct current voltage C₇₀. A product signalprovided by multiplier 431 is summed with another direct current voltageC₆₇ and the signal from multiplier 423 by summing means 433 to provide asignal corresponding to the term -C₆₇ -C₇₀ (API) (VI)-C₇₃ (W)(KV₂₁₀). Amultiplier 435 effectively squares signal API an provides it to amultiplier 437 where it is multiplied with a direct current voltage C₇₁.Multipler 437 provides a signal C₇₁ (API)². Summing means 440 sums thesignal from multipliers 420, 425, 428 & 437. Subtracting means 441subtracts the signal provided by summing means 433 from the signalprovided by summing means 440 to provide signal E₂₃.

FIG. 21 shows A computer 104 having a multiplier 445 effectivelysquaring signal KV₂₁₀ to provide a signal which is multiplied with adirect current voltage C₇₅ by a multiplier 446 which provides a signalcorresponding to the term C₇₅ (KV₂₁₀)² in equation 21. Multiplier 448multiplies signals KV₂₁₀, S to provide a signal that is multiplied witha direct current voltage C₇₉ by a multiplier 450. Multiplier 450provides a signal corresponding to the term C₇₉ (KV₂₁₀) (S) in equation21. A multiplier 453 multiplies signals API, FL to provide a signal toanother multiplier 454 where it is multiplied by a direct currentvoltage C₇₈. Multiplier 454 provides the signal corresponding to theterm C₇₈ (FL) (API) in equation 21. Summing means 456 essentially sumsall of the negative terms in equation 21 by summing the signals frommultipliers 446, 450 and 454. A multiplier 459 multiplies signal S witha direct current voltage C₇₆ to provide a signal corresponding to theterm C₇₆ (S) in equation 21. Another multiplier 460 effectively squaressignal FL and provides it to yet another multiplier 461 where it ismultiplied with a direct current voltage C₇₇. Multiplier 461 provides asignal corresponding to the term C₇₇ (FL)². Summing means 465essentially sums the positive terms of equation 21 by summing a directcurrent voltage C₇₄ with the signals provided by multipliers 459 and461. Subtracting means 467 subtracts the signal provided by summingmeans 456 from the signal provided by summing means 465 to providesignal E₂₆.

Referring now to FIG. 22, J computer 107 includes a square root circuit470 receiving signal T and providing a signal to a multiplier 471 whereit is multiplied with a direct current voltage C₈₁ to provide a signalto subtracting means 472. Subtracting means 472 subtracts a signalprovided by multiplier 471 from signal E₂₅ to provide a signalcorresponding to the term ΔVI-C₈₁ √T in equation 22. Subtracting means472 provides a signal to another subtracting means 473 which subtracts adirect current voltage C₈₀ to provide a signal corresponding to the term(ΔVI-C₈₀ -C₈₁ √T) in equation 22. A multiplier 476 multiplies signal Twith a direct current voltage C₈₂ to provide a signal corresponding tothe term C₈₂ T in equation 22. Another multiplier 480 multiplies signalT with signal E₂₆ to provide a signal to another multiplier 482 where itis multiplied with a direct current voltage C₈₃. Multiplier 482 providesa signal corresponding to the term C₈₃ (A) (T) in equation 22.Subtracting means 485 subtracts the product signal from multiplier 476from the signal from multiplier 482 to provide a signal which is dividedinto the signal provided by subtracting means 473 by a divider 487.Divider 487 provides signal E₂₇.

Referring to FIG. 23, J computer 110 includes a square root circuit 490receiving signal T and providing a signal to a multiplier 491 where itis multiplied with signal E₂₆. Multiplier 491 provides a signal toanother multiplier 492 where it is multiplied with a direct currentvoltage C₈₇ to provide a signal corresponding to the term C₈₇ (A)(T) inequation 23. Subtracting means 493 subtracts the direct current voltageC₈₆ from the signal from multiplier 492 to provide a difference signal.Subtracting means 494 subtracts signal E₂₅ from the difference signalprovided by subtracting means 493.

A multiplier 495 multiplies signals T and E₂₆ to provide a signal toanother multiplier 496 where it is multiplied with direct currentvoltage C₈₅. Multiplier 496 provides a signal, corresponding to the term[C₈₅ (A) (T)] in equation 23, to multipliers 500 and 501. Multiplier 500multiplies the signal from multiplier 496 with direct current voltage V₄to provide a signal to multiplier 505 where it is multiplies with thesignal from subtracting means 494. Multiplier 501 multiplies the signalfrom multiplier 496 with voltage V₂₃.

A multiplier 506 multiplies signal E₂₆ with a direct current voltage C₈₄to provide a signal to a multiplier 507 which effectively squares thesignal. Multiplier 507 provides a signal corresponding to the term [C₈₄(A)]² in equation 23. Subtracting means 510 subtracts the signalprovided by multiplier 505 from the signal provided by multiplier 507 toprovide a signal to square root circuit 512. Subtracting means 514subtracts the signal provided by square root circuit 512 to develop asum signal. A divider 515 divides the sum signal from summing means 514with the signal from multiplier 501 to provide a signal that is squaredby a multiplier 517 which provides signal E₂₈.

Selection means 81 in FIG. 24 includes comparators 520, 521 and 522.Comparator 520 compares signal S with a reference voltage VR₁corresponding to a predetermined percent sulfur content of the chargeoil, preferably about 1.0%, to determine whether the charge oil is sweetor sour. For sweet charge oil, comparator 520 provides a high leveloutput, while for sour charge oil it provides a low level output. Theoutput from comparator 520 is applied to an inverter 525 and to ANDgates 527, 528 and 529.

Comparators 521 and 522 compare signal KV₂₁₀ with reference voltages VR₂and VR₃ corresponding to predetermined kinetic viscosities, preferablyabout 7.0 and 15.0, respectively, and they determine whether the chargeoil is light, medium or heavy. For light charge oil, comparators 521,522 both provide high level outputs. For medium charge oil, comparators521 and 522 provide a low level output and a high logic level output,respectively. For heavy charge oil, comparators 521 and 522 provide lowlevel outputs.

Comparator 520 provide its output to an inverter 525 and to AND gates527, 528 and 529. Comparator 521 provides its output to an inverter 530and to AND gates 527 and 532. Comparator 522 provides its output toinverter 534 to AND gates 527, 528, 532 and 535. Inverter 525 providesits output to AND gates 532, 535 and 536. Inverter 530 provides itsoutput to AND GATES 528, 529, 535 and 536. Inverter 534 provides itsoutput to AND gates 529 and 536.

AND gates 527, 528, 529, 532, 535 and 536 decode the outputs ofcomparators 520, 521 and 522 and inverters 525, 530 and 534 to controlswitches 540 through 546 respectively, receiving signals E₁₃, E₂₁, E₂₇,E₁₅, E₂₂ and E₂₈, respectively. A high logic level (H) output from anAND gate renders a corresponding switch conductive to provide the signalthe switch receives as signal E₁₄. A low logic level (L) output from theAND gate renders the switch nonconductive. The following tablecorrelates the logic level of the AND gates to the type of charge oil.

    ______________________________________                                        CHARGE   AND GATES                                                            OIL      527     528     529   532   535   536                                ______________________________________                                        LIGHT                                                                         SWEET    H       L       L     L     L     L                                  LIGHT                                                                         SOUR     L       L       L     H     L     L                                  MEDIUM                                                                        SWEET    L       H       L     L     L     L                                  MEDIUM                                                                        SOUR     L       L       L     L     H     L                                  HEAVY                                                                         SWEET    L       L       H     L     L     L                                  HEAVY                                                                         SOUR     L       L       L     L     L     H                                  ______________________________________                                    

The present invention is hereinbefore described as a control system andmethod for controlling the operation of a furfural refining unit as afunction of certain quality factors of the charge oil being provided toit. More specifically, the unit is controlled as a function of the APIgravity, the flash point, the kinematic viscosity corrected to 210° F.and at 150° F., the refractive index and the sulfur content of thecharge oil to achieve more accurate control of the finished productbeing provided by the solvent refining unit.

It would be obvious to one skilled in the art, that the charge oil flowrate may be constant and the furfural flow rate varied. For thiscondition, equation 13 is rewritten as:

    24. SO=(CHG)(J)/100,

where SO is the new furfural flow rate. Of course, elements 84 and 85would have to be re-arranged so that signal E₁₄ is multiplied withsignal CHG and the product signal divided by voltage V₂ to providesignal SO to a flow rate controller controlling a valve in line 7.

We claim:
 1. A control system for a furfural refining unit receivingcharge oil and furfural solvent, one of which is maintained at a fixedflow rate while the flow rate of the other is controlled by the controlsystem, treats the received charge oil with the received furfural toyield means for sampling the charge oil and providing a signal APIcorresponding to the API gravity of the charge oil, flash point analyzermeans for sampling the charge oil and providing a signal FLcorresponding to the flash point temperature of the charge oil,viscosity analyzer means for sampling the charge oil and providingsignals KV₁₅₀ and KV₂₁₀ corresponding to the kinematic viscosities,corrected to 150° F. and 210° F., respectively, sulfur analyzer forsampling the charge oil and providing a signal S corresponding to thesulfur content of the charge oil, a refractometer samples the charge oiland provides a signal RI corresponding to the refractive index of thecharge oil, flow rate sensing means for sensing the flow rates of thecharge oil and of the furfural and providing signals CHG and SOLV,corresponding to the charge flow rate and the furfural flow rate,respectively, means for sensing the temperature of the extract-mix andproviding a corresponding signal T, and control means connected to allof the analyzer means, the refractometer, and to all the sensing meansfor controlling the other flow rate of the charge oil and the furfuralflow rates in accordance with signals API, FL, KV₁₅₀, KV₂₁₀, S, RI, CHG,T and SOLV.
 2. A system as described in claim 1, in which the charge oilmay be light sweet charge oil having a sulfur content equal to or lessthan a predetermined sulfur content and having a kinematic viscosity,corrected to a predetermined temperature, equal to or less than a firstpredetermined kinematic viscosity, light sour charge oil having a sulfurcontent greater than the predetermined sulfur content and having akinematic viscosity, corrected to the predetermined temperature, equalto or less than the first predetermined kinematic viscosity, mediumsweet charge oil having a sulfur content equal to or less than thepredetermined sulfur content and having a kinematic viscosity, correctedto the predetermined temperature, greater than the first predeterminedkinematic viscosity but equal to or less than a second predeterminedkinematic viscosity, medium sour charge oil having a sulfur contentgreater than the predetermined sulfur content and having a kinematicviscosity, corrected to the predetermined temperature, greater than thefirst predetermined kinematic viscosity but equal to or less than thesecond predetermined kinematic viscosity, heavy sweet charge oil havinga sulfur content equal to or less than the predetermined sulfur contentand having a kinematic viscosity, corrected to the predeterminedtemperature, greater than the second predetermined kinematic viscosity,or heavy sour charge oil having a sulfur content greater than thepredetermined sulfur content and having a kinematic viscosity, correctedto the predetermined temperature, greater than the second predeterminedkinematic viscosity; and the control means includes a plurality of Jsignal means, each J signal means providing a signal J representative ofa furfural dosage for a corresponding type of charge oil, selectionmeans connected to the J signal means, to the viscosity analyzing meansand to the sulfur analyzing means for selecting on of the J signals inaccordance with one of the kinetic viscosity signals from the viscosityanalyzer means and signal S and providing the selected J signal, controlsignal means connected to the selection means and to the flow ratesensing means for providing a control signal in accordance with theselected J signal and one of the sensed flow rate signals, and apparatusmeans connected to the control network means for controlling the oneflow rate of the charge oil and furfural flow rates in accordance withthe control signal.
 3. A system as described in claim 2, in which thecontrol means includes VI signal means connected to the viscosityanalyzer means for providing a signal VI corresponding to the viscosityindex of the charge oil in accordance with kinematic viscosity signalsKV₁₅₀ and KV₂₁₀ ; SUS₂₁₀ signal means connected to the viscosityanalyzer means for providing a signal SUS₂₁₀ corresponding to the chargeoil viscosity in Saybolt Universal Seconds corrected to 210° F; W signalmeans connected to the viscosity analyzer means, to the gravity analyzermeans and to the sulfur analyzer means for providing a signal Wcorresponding to the wax content of the charge oil in accordance withsignals KV₂₁₀, API and S, first A signal means connected to theviscosity analyzer means, to the sulfur analyzer means, to the flashpoint temperature analyzer means, to the gravity analyzer means and tothe VI signal means for providing a first signal A corresponding to aninterim factor A in accordance with signals KV₂₁₀, S, FL, API and VI;second A signal means connected to the viscosity analyzer means, to thegravity analyzer means and to the flash point temperature analyzer meansfor providing a second signal A corresponding to an interim factor A inaccordance with signals KV₂₁₀, API and FL; third A signal meansconnected to the gravity analyzer means, to the viscosity analyzermeans, to the sulfur analyzer means, to the flash point temperatureanalyzer means and to the VI signal means for providing a third signal Acorresponding to an interim factor A in accordance with signals KV₂₁₀,S, API, VI and FL; first ΔVI signal means connected to the viscosityanalyzer means, to the gravity analyzer means, to the flash pointtemperature analyzer means, to the VI signal means and to the SUS₂₁₀signal means and receiving a direct current voltage VI_(RP)corresponding to the viscosity index of the refined oil at thepredetermined temperature for providing a first signal ΔVI in accordancewith signals KV₂₁₀, API, FL, VI and SUS₂₁₀ and voltage VI_(RP) ; secondΔVI signal means connected to the gravity analyzer means, to the flashpoint temperature analyzer means, to the refractometer, to the VI signalmeans, to the W signal means and to the SUS₂₁₀ signal means andreceiving voltage VI_(RP) for providing a second signal ΔVIcorresponding to the change in viscosity index in accordance withsignals VI, W, API, FL, RI, SUS₂₁₀ and voltage VI_(RP) ; third ΔVIsignal means connected to the viscosity analyzer means, to the gravityanalyzer means, to the flash point temperature analyzer means, to the VIsignal means, the W signal means and the SUS₂₁₀ signal means andreceiving voltage VI_(RP) for providing a third signal ΔVI correspondingto the change in viscosity index in accordance with signals KV₂₁₀, API,VI, FL, W and SUS₂₁₀ and voltage VI_(RP) ; and the plurality of J signalmeans includes first J signal means connected to the first ΔVI signalmeans, to the first A signal means, to the temperature sensing means andto the selection means for providing a first J signal to the selectionmeans corresponding to a furfural dosage for light sweet charge oil inaccordance with the first ΔVI signal, the first signal A and signal T,second J signal means connected to the first ΔVI signal means, to thefirst A signal means, to the temperature sensing means and to theselection means for providing a second J signal to the selection meanscorresponding to the furfural dosage for light sour charge oil inaccordance with the first signal ΔVI, the first signal A and signal T,third J signal means connected to the second ΔVI signal means, to thesecond A signal means, to the temperature sensing means and to theselection means for providing a third J signal to the selection meanscorresponding to the furfural dosage for medium sweet charge oil inaccordance with the second signal ΔVI, the second signal A, and signalT, fourth J signal means connected to the second ΔVI signal means, tothe temperature sensing means and to the selection means for providing afourth J signal to the selection means corresponding to the furfuraldosage for medium sour charge oil in accordance with the second signalΔVI and signal T, fifth J signal means connected to the third ΔVI signalmeans, to the third A signal means, to the temperature sensing means andto the selection means for providing a fifth signal J to the selectionmeans corresponding to the furfural dosage for heavy sweet charge oil inaccordance with the third signal ΔVI, the third signal A and signal T,and sixth J signal means connected to the third ΔVI signal means, to thethird A signal means, to the temperature sensing means and to theselection means for providing a sixth J signal to the selection means inaccordance with the third signal ΔVI, the third signal A and signal T.4. A system as described in claim 3 in which the SUS₂₁₀ signal meansincludes SUS signal means connected to the viscosity analyzer means, andreceiving direct current voltages C₅ through C₁₂ for providing a signalSUS corresponding to an interim factor SUS in accordance with signalKV₂₁₀, voltages C₅ through C₁₂ and the following equation:

    SUS=C.sub.5 (KV.sub.210)+[C.sub.6 +C.sub.7 (KV.sub.210)]/[C.sub.8 +C.sub.9 (KV.sub.210)+C.sub.10 (KV.sub.210).sup.2 +C.sub.11 (KV.sub.210).sup.3 ](C.sub.12),

where C₅ through C₁₂ are constants; and SUS₂₁₀ network means connectedto the SUS signal means and to all the ΔVI signal means and receivingdirect current voltages C₁₃ through C₁₆ for providing signal SUS₂₁₀ toall the ΔVI signal means in accordance with signal SUS, voltages C₁₃through C₁₆ and the following equation:

    SUS.sub.210 =[C.sub.13 +C.sub.14 (C.sub.15 -C.sub.16)]SUS,

where C₁₃ through C₁₆ are constants.
 5. A system as described in claim 4in which the W signal means further receives direct current voltages C₄₃through C₄₉ and provides signal W in accordance with signals API, KV₂₁₀and S, voltages C₄₃ through C₄₉, and the following equation:

    W=C.sub.43 -C.sub.44 API+C.sub.45 /KV.sub.210 -C.sub.46 S+C.sub.47 (API).sup.2 -C.sub.48 API/KV.sub.210 +C.sub.49 (S)(API).sub.s

where C₄₃ through C₄₉ are constants.
 6. A system as described in claim 5in which the VI signal means includes K signal means receiving directcurrent voltages C₂, C₃, C₄ and T₁₅₀ for providing a signal K₁₅₀corresponding to the kinematic viscosity of the charge oil corrected to150° F. in accordance with voltages C₂, C₃, C₄ and T₁₅₀, and thefollowing equation:

    K.sub.150 =[C.sub.2 -In(T.sub.150 +C.sub.3)]/C.sub.4,

where C₂ through C₄ are constants, and T₁₅₀ corresponds to a temperatureof 150° F.; H₁₅₀ signal means connected to the viscosity analyzer meansand receiving a direct current voltage C₁ for providing a signal H₁₅₀corresponding to a viscosity H value for 150° F. in accordance withsignal KV₁₅₀ and voltage C₁ in the following equation:

    H.sub.150 =lnln(KV.sub.150 +C.sub.1),

where C₁ is a constant; H₂₁₀ signal means connected to the viscosityanalyzer means and receiving voltage C₁ for providing signal H₂₁₀corresponding to a viscosity H value for 210° F. in accordance withsignal KV₂₁₀, voltage C₁ and the following equation:

    H.sub.210 =lnln(KV.sub.210 +C.sub.1),

H₁₀₀ signal means connected to the K signal means, to the H₁₅₀ signalmeans and the H₂₁₀ signal means for providing a signal H₁₀₀corresponding to a viscosity H value for 100° F., in accordance withsignals H₁₅₀, H₂₁₀ and K₁₅₀ and the following equation:

    H.sub.100 =H.sub.210 +(H.sub.150 -H.sub.210)/K.sub.150

kv₁₀₀ signal means connected to the H₁₀₀ signal means and receivingvoltage C₁ for providing a signal KV₁₀₀ corresponding to a kinematicviscosity for the charge oil corrected to 100° F. in accordance withsignal H₁₀₀, voltage C₁, and the following equation:

    KV.sub.100 =exp[exp(H.sub.100)]-C.sub.1,

and VI memory means connected to the KV₁₀₀ signal means and to theviscosity analyzer means having a plurality of signals stored therein,corresponding to different viscosity index and controlled by signalsKV₁₀₀ and KV₂₁₀ to select a stored signal and providing the selectedstored signal as signal VI.
 7. A system as described in claim 6 in whichthe first A signal means also receives direct current voltages C₂₄through C₃₁ and provides the first signal A in accordance with signalsS, KV₂₁₀, API, VI and FL, voltages C₂₄ through C₃₁ and the followingequation:

    A=C.sub.24 -C.sub.25 (S)-C.sub.26 (S).sup.2 +C.sub.27 (KV.sub.210)(API)-C.sub.28 (KV.sub.210)(VI)-C.sub.29 (FL)(API)+C.sub.30 (FL)(S)+C.sub.31 (FL)(VI),

where C₂₄ through C₃₁ are constants.
 8. A system as described in claim 7in which the second A signal means also receives direct current voltagesC₅₅ through C₅₆ and provides the second A signal in accordance withsignals API, FL, and KV₂₁₀, voltages C₅₅ through C₅₇ and the followingequation:

    A=C.sub.55 -C.sub.50 (API)+C.sub.57 (FL)(KV.sub.210),

where C₅₅ through C₅₇ are constants.
 9. A system as described in claim10 in which the third A signal means also receives direct currentvoltages C₇₄ through C₇₉ and provides the third signal A in accordancewith signals KV₂₁₀, S, FL, and API, voltages C₇₄ through C₇₉, and thefollowing equation:

    A=C.sub.74 -C.sub.75 (KV.sub.210).sup.2 +C.sub.76 (S)+C.sub.77 (FL).sup.2 -C.sub.78 (FL)(API)-C.sub.79 (KV.sub.210)(S),

where C₇₄ through C₇₉ are constants.
 10. A system as described in claim9 in which the first ΔVI signal means includes VI_(DWC).sbsb.O signalmeans connected to the flash point temperature analyzer means, to theviscosity analyzer means and to the gravity analyzer means, and to theVI signal means, and receiving direct current voltages C₁₇ through C₂₀for providing a first signal VI_(DWC).sbsb.O corresponding to theviscosity index of the dewaxed charge oil for 0° F. in accordance withsignals FL, VI, KV₂₁₀ and API, voltages C₁₇ through C₂₀ and thefollowing equation:

    VI.sub.DWC.sbsb.O =C.sub.17 -C.sub.18 (FL)+C.sub.19 (VI)+C.sub.20 (KV.sub.210)(API),

where C₁₇ through C₂₀ are constants; VI_(DWC).sbsb.P signal meansconnected to the first VI_(DWC).sbsb.O signal means and to the SUS₂₁₀signal means, and receiving direct current voltages C₂₁ through C₂₃ andPour, providing a signal VI_(DWC).sbsb.P corresponding to the viscosityindex of the dewaxed charge oil at the predetermined temperature, inaccordance with signals VI_(DWC).sbsb.O and SUS₂₁₀, voltages C₂₁ throughC₂₃ and Pour, and the following equation:

    VI.sub.DWC.sbsb.P =VI.sub.DWC.sbsb.O +(POUR)[C.sub.21 -C.sub.22 lnSUS.sub.210 +C.sub.23 (lnSUS.sub.210).sup.2 ],

where Pour is the pour point of the dewaxed product and C₂₁ through C₂₃are constants; subtracting means connected to the first VI_(DWC).sbsb.Pmeans and to the first and second J signal means and receiving voltageVI_(RP) for kinematic voltage VI_(RP) from signal VI_(DWC).sbsb.P toprovide the first ΔVI signal to the first and second J signal means. 11.A system as described in claim 10 in which the second ΔVI signal meansincludes a second VI_(DWC).sbsb.O signal means connected to the gravityanalyzer means, the flash point temperature analyzer means, therefractometer, the VI signal means and the W signal means, and receivesdirect current voltages C₅₀ through C₅₄ and provides a secondVI_(DWC).sbsb.O signal in accordance with signals RI, VI, FL, W and API,voltages C₅₀ through C₅₄ and the following equation:

    VI.sub.DWC.sbsb.O =C.sub.50 -C.sub.51 RI+C.sub.52 (RI)(VI)+C.sub.53 (FL)(API)-C.sub.54 (W)(VI),

where C₅₀ through C₅₄ are constants; a second VI_(DWC).sbsb.P signalmeans connected to the second VI_(DWC).sbsb.O signal means and to theSUS₂₁₀ signal means for providing a second VI_(DWC).sbsb.P signal inaccordance with signals SUS₂₁₀ and VI_(DWC).sbsb.O, voltages C₂₁ throughC₂₃ and Pour, and the following equation:

    VI.sub.DWC.sbsb.p =VI.sub.DWC.sbsb.O +(POUR)[C.sub.21 -C.sub.22 lnSUS.sub.210 +C.sub.23 (lnSUS.sub.210).sup.2 ],

and second subtracting means connected to the third and fourth J signalmeans and to the second VI_(DWC).sbsb.P signal means and receivingvoltage VI_(RP) for subtracting signal VI_(DWC).sbsb.P from voltageVI_(RP) to provide the second ΔVI signal to the third and fourth Jsignal means.
 12. A system as described in claim 11 in which the thirdΔVI signal means includes a third VI_(DWC).sbsb.O signal means connectedto the viscosity analyzer means, to the gravity analyzer means, to theflash point temperature analyzer means, to the VI signal means, to the Wsignal means and receiving direct current voltages C₆₇ through C₇₃ forproviding a third signal VI_(DWC).sbsb.O in accordance with signalsKV₂₁₀, VI, API, FL and W, voltages C₆₇ through C₇₃, and the followingequation:

    VI.sub.DWC.sbsb.O =-C.sub.67 +C.sub.68 (KV.sub.210).sup.2 +C.sub.69 (VI)-C.sub.70 (API)(VI)+C.sub.71 (API).sup.2 +C.sub.72 (FL)(VI)-C.sub.73 (W)(KV.sub.210),

where C₆₇ through C₇₃ are constants; a third VI_(DWC).sbsb.P signalmeans connected to the third VI_(DWC).sbsb.O signal means and to theSUS₂₁₀ signal means, and receiving direct current voltages C₂₁ throughC₂₃ and Pour, for providing a third signal VI_(DWC).sbsb.P in accordancewith signal VI_(DWC).sbsb.O and SUS₂₁₀, voltages C₂₁ through C₂₃, andPour, and the following equation:

    VI.sub.DWC.sbsb.P =VI.sub.DWC.sbsb.O +(POUR)[C.sub.21 -C.sub.22 lnSUS.sub.210 +C.sub.23 (lnSUS.sub.210).sup.2 ],

and third subtracting means connected to the third VI_(DWC).sbsb.Psignal means and to the fifth and sixth J signal means and receivingdirect voltage VI_(RP) for subtracting the third signal VI_(DWC).sbsb.Pfrom voltage VI_(RP) to provide the third ΔVI signal to the fifth andsixth J signal means.
 13. A system as described in claim 12 in whichflow rate of the charge oil is controlled and the flow of the furfuralis maintained at a constant rate and the control signal means receivessignal SOLV from the flow rate sensing means, the selected J signal fromthe selection means and a direct current voltage corresponding to avalue of 100 and provides a signal C to the apparatus meanscorresponding to a new charge oil flow rate in accordance with theselected J signal, signal SOLV and the received voltage and thefollowing equation:

    C=(SOLV)(100)/J,

so as to cause the apparatus means to change the charge oil flow to thenew flow rate.
 14. A system as described in claim 12 in which thecontrolled flow rate is the furfural flow rate and the flow of thecharge oil is maintained constant, and the control signal means isconnected to the sensing means, to the selection means and receives adirect current voltage corresponding to the value of 100 for providing asignal SO corresponding to a new furfural flow rate in accordance withsignals CHG and the selected J signal and the received voltage, and thefollowing equation:

    SO=(CHG)(J)/100,

so as to cause the furfural flow to change to the new flow rate.
 15. Acontrol system as described in claim 12 in which the first J signalmeans also receives direct current voltages C₃₂ through C₃₉ and providesthe first J signal in accordance with signal T, the first A signal andthe first ΔVI signal, voltages C₃₂ through C₃₉ and the followingequation:

    J={{C.sub.32 -C.sub.33 A+{[C.sub.33 A-C.sub.32 ].sup.2 -4[C.sub.34 -C.sub.35 A][-C.sub.36 +C.sub.37 √T-C.sub.38 (A)(√T)-ΔVI]}.sup.1/2 }/2[C.sub.34 -C.sub.35 (A)]}.sup.2,

where C₃₂ through C₃₉ are constants; the second J signal means alsoreceives direct current voltages C₃₉ through C₄₂ and provides the secondJ signal in accordance with signal T, and the first ΔVI signal, voltagesC₃₉ through C₄₂ and the following equation:

    J={{-C.sub.39 +{(C.sub.39).sup.2 -4(C.sub.40)(T)[-C.sub.41 +C.sub.42 T-ΔVI]}.sup.1/2 }/2(C.sub.40 T)}.sup.2,

where C₃₉ through C₄₂ are constants; the third J signal means alsoreceives direct current voltages C₅₈ through C₆₁ and provides the thirdJ signal in accordance with signal T, the second A signal and the secondΔVI signal, voltages C₅₈ through C₆₁ and the following equation:

    J={{-C.sub.58 A+{(C.sub.58 A).sup.2 -4C.sub.59 A(C.sub.60 +C.sub.61 √T-ΔVI)}.sup.1/2 }/2C.sub.59 A}.sup.2,

where C₅₈ through C₆₁ are constants; the fourth J signal means alsoreceives direct current voltages C₆₂ through C₆₆ and provides the fourthJ signal in accordance with signal T, the second A signal and the secondΔVI signal, voltages C₆₂ through C₆₆ and the following equation:

    J={{-C.sub.62 +{(C.sub.62).sup.2 -4(-C.sub.63)[C.sub.64 √T+C.sub.65 (√T)(A)-C.sub.66 -ΔVI]}.sup.1/2 }/2C.sub.63 }.sup.2,

where C₆₂ through C₆₆ are constants; the first J signal means alsoreceives direct current voltages C₈₀ through C₈₃ and provides the fifthJ signal in accordance with signal T, the third A signal and the thirdΔVI signal, voltages C₈₀ through C₈₃ and the following equation:

    J=(ΔVI-C.sub.80 -C.sub.81 √T)/[-C.sub.82 T+C.sub.83 (A)(T)],

where C₈₀ through C₈₃ are constants; the sixth J signal means alsoreceives direct current voltages C₈₄ through C₈₇ and provides the sixthJ signal in accordance with signal T, the third A signal and the thirdΔVI signal, voltages C₈₁ through C₈₇ and the following equation:

    J={{-C.sub.84 A+{[C.sub.84 (A)].sup.2 -4[C.sub.85 (A)(T)][-C.sub.86 +C.sub.87 (A)(√T)-ΔVI]}.sup.1/2 }/2[C.sub.85 (A)(T)]}.sup.2,

where C₈₄ through C₈₇ are constants.